Multi-Stage Chemical Flotation of Food Packaging Prints

The use of packaging prints in the production of graphic paper grades was studied. The input combination of cardboard food packaging prints (full colour CMYK) together with office laser prints was used for the production of recovered handsheets. The aim of the study was to evaluate the efficacy of conventional chemical deinking multi-stage flotation on each of the input material as well as on their combination. One side coated cardboard was printed with offset inks and finished with an UV varnish layer. After the first flotation stage the repeated flotation was done and the handsheets were produced before and after each flotation. The flotation froth was collected during both flotation stages in order to be flotated itself. The flotation efficacy was evaluated by the means of ISO whiteness in comparison with particle size distribution. Also the measurements of ash content were compared to the results of mechanical properties of the handsheets. The results of the study show that the optical properties of the handsheets increase by the addition of the office laser prints in the input material. For all the input materials and their combination the first flotation stage was the most efficient one. The second flotation stage influenced the additional increase in whiteness only slightly. The particle size distribution correlates to the achieved results, particularly if the measurement range was adjusted to the narrower threshold scale. LM images show that the cardboard coating layer did not disintegrate completely, and the particles of non-disintegrated coating layer are visible. Their white colour makes them invisible on scans prepared for image analyzer. The presence of coating layer particles as well as fillers was identified by ash content measurements. The decrease in ash content correlates to the increase of breaking length for all the samples. The results of study showed that combination sample characteristics are more similar to office laser prints sample characteristics than to mean of summed up values of input material characteristics.